Overview

Commits are made using the commit queue, which triggers a series of try jobs to compile and test the proposed patch against Chromium tip of tree before actually making the commit. If the try jobs succeed the patch is committed. A newly committed change triggers the builders (or “bots”) to compile and test the change again.

Bots

Bots are slaves attached to a buildbot master (or “waterfall”). A buildbot master is a server which polls for commits to a repository and triggers workers to compile and test new commits whenever they are detected. chromium.mac is the main waterfall for Mac desktop and iOS. tryserver.chromium.mac serves as the try server for Mac desktop and iOS.

The bots know how to check out a given revision of Chromium, compile, and test.

Code location

Master configs

The masters are configured in tools/build, a separate repository which contains various infra-related scripts.

Pollers

chromium.mac uses a GitilesPoller which polls the Chromium repository for new commits using the gitiles interface. When a new commit is detected, the bots are triggered.

Recipes

Configs

Because the recipes live in another repository, changes to the recipes don‘t go through the Chromium commit queue and aren’t tested on the try server. In order to allow bot changes to be tested by the commit queue, the recipes for iOS are generic instead of bot-specific, and rely on configuration files which live in master-specific JSON config files located in src/ios/build/bots. These configs define the gn_args to use during compilation as well as the tests to run.

Scripts

The test runner is the script which installs and runs the tests, interprets the results, and collects any files emitted by the test (“test data”). It can be found in src/ios/build/bots/scripts, which means changes to the test runner can be tested on the try server.

Compiling with goma

Goma is the distributed build system used by Chromium. It reduces compilation time by avoiding recompilation of objects which have already been compiled elsewhere.

Testing with swarming

Tests run on swarming, a distributed test system used by Chromium. After compilation, configured tests will be zipped up along with their necessary dependencies (“isolated”) and sent to the swarming server for execution. The server issues tasks to its attached workers for execution. The bots themselves don't run any tests, they trigger tests to be run remotely on the swarming server, then wait and display the results. This allows multiple tests to be executed in parallel.

Try bots

Try bots are bots which test proposed patches which are not yet committed.

Request try job access in order to trigger try jobs against your patch. The relevant try bots for an iOS patch are ios-device, ios-device-xcode-clang, ios-simulator, and ios-simulator-xcode-clang. These bots can be found on the Mac-specific try server. A try job is said to succeed when the build passes (i.e. when the bot successfully compiles and tests the patch).

ios-device and ios-device-xcode-clang both compile for the iOS device architecture (ARM), and neither run any tests. A build is considered successful so long as compilation is successful.

ios-simulator and ios-simulator-xcode-clang both compile for the iOS simulator architecture (x86), and run tests in the iOS simulator. A build is considered successful when both compilation and all configured test succeed.

ios-device and ios-simulator both compile using the version of clang defined by the CLANG_REVISION in the Chromium tree.

ios-device-xcode-clang and ios-simulator-xcode-clang both compile using the version of clang that ships with Xcode.

Scheduling try jobs using buildbucket

Triggering a try job and collecting its results is accomplished using buildbucket. The service allows for build requests to be put into buckets. A request in this context is a set of properties indicating things such as where to get the patch. The try bots are set up to poll a particular bucket for build requests which they execute and post the results of.

Compiling with the analyzer

In addition to goma, the try bots use another time-saving mechanism called the analyzer to determine the subset of compilation targets affected by the patch that need to be compiled in order to run the affected tests. If a patch is determined not to affect a certain test target, compilation and execution of the test target will be skipped.

Configuring the bots

See the configs code location for where to find the config files for the bots. The config files are JSON which describe how the bot should compile and which tests it should run. The config files are located in the configs directory. The configs directory contains a named directory for each master. For example:

$ ls ios/build/bots
OWNERS scripts tests chromium.fyi chromium.mac

In this case, configs are defined for iOS bots on chromium.fyi and chromium.mac. Inside each master-specific directory are JSON config files named after each bot. For example:

$ ls ios/build/bots/chromium.mac
ios-device.json ios-simulator.json

The ios-device bot on chromium.mac will read its configuration from chromium.mac/ios-device.json in the configs directory.

Example

The comments key is optional and defines a list of strings which can be used to annotate the config. You may want to explain why the bot exists and what it's doing, particularly if there are extensive and atypical gn_args.

The gn_args key is a required list of arguments to pass to GN to generate the build files. Two GN args are required, is_debug and target_cpu. Use is_debug to define whether to compile for Debug or Release, and target_cpu to define whether to compile for x86, x64, arm, or arm64. The iOS bots typically perform Debug builds for x86 and x64, and Release builds for arm and arm64. An x86/x64 build can only be tested on the iOS simulator, while an arm/arm64 build can only be tested on a physical device.

Since Chromium for iOS is shipped as a universal binary, it's also fairly common to set additional_target_cpus. For simulator builds, we typically set:

This dict says to run ios_chrome_unittests on an iPhone 5s running iOS 11.0 using Xcode build version 9A235. A test dict may optionally define a list of test args, which are arguments to pass directly to the test on the command line, and it may define a boolean value xctest to indicate whether the test is an xctest (default if unspecified is false). For example:

This defines two tests to run, first ios_chrome_unittests will be run with --foo and --bar passed directly to the test on the command line. Next, ios_chrome_integration_egtests will be run as an xctest. "xctest": true must be specified for all xctests, it is an error to try and launch an xctest as a regular test.

An include dict defines a list of tests to import from the tests subdirectory in the configs directory. For example:

Uploading compiled artifacts from a bot

A bot may be configured to upload compiled artifacts. This is defined by the upload key. For example:

{"comments":["Sample config for a bot which uploads artifacts."],"gn_args":["is_debug=true","target_cpu=\"x64\""],"upload":[{"artifact":"Chromium.breakpad","bucket":"my-gcs-bucket",},{"artifact":"Chromium.app","bucket":"my-gcs-bucket","compress":true,},{"artifact":"Chromium.breakpad","symupload":"https://clients2.google.com/cr/symbol",}]}

After compilation, the bot will upload three artifacts. First the Chromium.breakpad symbols will be uploaded to gs://my-gcs-bucket/<buildername>/<buildnumber>/Chromium.breakpad. Next Chromium.app will be tarred, gzipped, and uploaded to gs://my-gcs-bucket/<buildername>/<buildnumber>/Chromium.tar.gz. Finally the Chromium.breakpad symbols will be uploaded to the breakpad crash reporting server where they can be used to symbolicate stack traces.